[Decode]

likbez, мб так?

<form action="#">
  <input type="text" />
  <input type="submit" value="Send" />
  <span style="color:red;"></span>
</form>


<script>
  var formElem = document.body.children[0];
  var inpElem = formElem.elements[0];
  var reg = /^[а-я\s.]+?\d+/i;

  formElem.onsubmit = function() {
    if ( !reg.test(inpElem.value) ) {
      this.querySelector('span').innerHTML = 'Неверный формат';
      return false;
    }
  };
</script>